In the bowl of a food processor (or blender) add the pine nuts, basil leaves, garlic cloves, and cheese. Process the ingredients till finely chopped.
Pour the olive oil in slowly through the nozzle while the food processor is running on low speed and drizzle the oil in. Keep stopping to scrape the sides and keep processing until a smooth paste forms or until you get the paste you prefer.
Season with salt and pepper (if using) and transfer the pesto to an airtight container to store. Be sure to cover the pesto with enough oil before sealing this acts as a preservative sealing out the air.
